Prevailing torque nuts usually are a deformed version of a hexagonal nut for a bolt, stud or other externally threaded element, often with an integral flange washer, and the intention is for the binding and prevailing torque to take place between the threads of the nut and the bolt as the nut is threaded onto the bolt. Normally the nut is applied with a power wrench or by use of a manual torque wrench, and the person carrying out this operation will preset the wrench to a specified value in accordance with a tightening specification. If the assembly subsequently loosens, the nut will remain in place and will strongly resist being shaken loose through vibration because of the prevailing torque.
Although there are numerous methods available, many of which are patented, for applying a deformation to a hexagonal nut in order to deform it, or at least a portion of it, so that binding will take place between the nut and the bolt on which it is threaded, a satisfactory degree of consistency of deformation has been lacking with most techniques. This has meant that many of the produced nuts were rejects, as being either too greatly deformed or too little.
There has recently been developed a technique for making prevailing torque nuts which provides a substantial degree of consistency at least for a limited number of nuts. This technique is described and claimed in copending U.S. application Ser. No. 447,411 filed Dec. 6, 1982, and now U.S. Pat. No. 4,509,220, entitled Prevailing Torque Nut naming David C. Cooper and Kenneth J. Bouchard as inventors and assigned to the same assignee as this application.
The previously invented technique provides a method of making a prevailing torque nut from a regular nut, comprising the steps of placing the regular nut between two jaw members, then decreasing the gap between the jaw members so that they contact the nut, and then further decreasing the gap between the jaw members by a preset amount to permanently inwardly deform the nut.
The previously invented technique also provides an apparatus for converting regular nuts to prevailing torque nuts. The apparatus includes two jaw members and delivery means for placing the regular nuts sequentially between the jaw members. Power means are provided for controlling the spacing between the jaw members such that the jaw members first come into contact with opposite sides of the nut located between them, and then the spacing between the jaw members is decreased by a predetermined amount which is the same for all nuts.
A disadvantage of the aforementioned technique described and claimed in the aforesaid application results from the fact that the preset or predetermined amount is governed by the spacing between two movable members which move towards each other with the jaw members and then strike and abut each other to cause further closing movement of the jaws to cease. The repeated striking together of these movable members ultimately results in changes in the preset amount taking place and, therefore, from time-to-time the movable members must be readjusted relative to each other and even replaced.
It also has been demonstrated that the process of the instant invention is faster and more accurate than the aforementioned technique and has greater flexibility and repeatability.